1. Field of the Invention
The present invention relates generally to measuring devices for measuring aspects of objects, and more particularly to a measuring device for ultra-precise measuring aspects of objects.
2. Discussion of the Related Art
Referring to FIG. 10, a typical measuring device 90 includes a magnetic core 91, a coil 92, a fulcrum 93, a level 94, and a measuring tip 95. A distal end of the measuring tip 95 always contacts with a surface of a workpiece 96. A typical contour measuring method using the measuring device 90 includes the following steps: (1) driving the workpiece 96 to move along an X-axis; (2) the measuring tip 95 moves along a Z-axis because the workpiece 96 has a curved surface, thus the level 94 rotates about the fulcrum 93; (3) the magnetic core 91 moves in the coil 92, this movement of the magnetic core 91 induces a current in the coil 92; (4) The current flows into the managing circuit 97 and the managing circuit 97 amplifies and transforms the current into a digital value that is used as a signal to the computer 98; (5) the computer 98 calculates a displacement of the magnetic core 91 according to the digital signal, thus indirectly determining a displacement of the measuring tip 95.
However, the above-described measuring device has the following disadvantages. Firstly, cumulative errors may generate and propagate from the coil 92, and in each of the conversions, to the computer calculation of the displacement of the core 91. Thus, a cumulative error is very large in the contour measuring method. Secondly, a non-linear error is generated when the coil 92 works in a non-linear region of the coil 92. Thirdly, the measuring range is very small because of the non-linear region of the coil 92. Finally, in order to measure the lower surface of the workpiece 96, the workpiece 96 should be turned over. This turning over and repositioning of the workpiece 96 may result in the workpiece 96 being repositioned outside of the original position, thus the measuring precision further decreases.
Therefore, a measuring device for measuring aspects of objects which have high precision are desired.